V-ribbed belt and method for manufacturing same

ABSTRACT

A V-ribbed belt that includes a ribbed surface covered with fabric is provided. The fabric is stretchable in two predetermined directions. A method for manufacturing the V-ribbed belt is also provided. The method includes placing a belt matrix about a mandrel, placing a fabric about the external circumference of the belt matrix which wraps around the mandrel, placing the mandrel inside a shell having a plurality of grooves on the internal circumference, expanding the belt matrix and the fabric toward the internal circumference of the shell and thus pressing the fabric onto the internal circumference having the multi-ribbed structure, and curing the belt matrix with the fabric. The fabric is stretchable to accommodate itself to the multi-ribbed structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of International ApplicationPCT/JP2008/058895 filed on May 8, 2008, which claims the benefit ofJapanese Patent Application No. 2007-239003 filed on Sep. 14, 2007, bothof which are hereby incorporated herein by reference in their entirety.

BACKGROUND

The present invention relates to a V-ribbed belt which is applied inmechanical power transmission, and a method for manufacturing such aV-ribbed belt.

As for the method of manufacturing a V-ribbed belt, the following twoare known. In one method, a rubber matrix arranged around a mold iscured, and then the belt surface thereof is ground to form ribs. Inanother method, i.e., in the so-called molding method, a rubber matrixis molded in a mold having a predetermined multi-ribbed structure andvulcanized or cured whereby a plurality of ribs is formed. The basiccharacteristics of a belt with the rib rubber material exposed on therib surface, such as its power transmission performance, its slip noiseproperties and so on, are mainly determined by the physical propertiesof the materials on the rib surface, which in turn is affected by therib rubber material and materials compounded into the rib rubbermaterial, such as short fibers, etc. However, the rib surfacedeteriorates over time due to wear. In an application of the moldingmethod, some types of belts are provided with a non-woven fabric on therib surface as disclosed in PCT Japanese Translation Patent PublicationNo. 2005-532513, but these lack durability.

SUMMARY

In the case of a conventional power transmission belt as describedabove, such as the conventional V-ribbed belt, the rib surface isvulnerable to wear, making it difficult to maintain in a stable state.Furthermore, the coefficient of friction tends to increase with use andthis may increase the production of noise.

Therefore, an object of the present invention is to improve thedurability of the rib surface of a V-ribbed belt as well as to prolongthe desired condition of the rib surface.

According to an aspect of the present invention, a V-ribbed beltincluding a rib surface covered with fabric is provided. The fabric isstretchable in two predetermined directions.

According to another aspect of the present invention, a method formanufacturing the V-ribbed belt is provided. The method includes placinga belt matrix about a mandrel, placing a fabric about the externalcircumference of the belt matrix, which wraps around the mandrel,placing the mandrel inside a shell having a plurality of grooves on theinternal circumference, expanding the belt matrix and the fabric towardthe internal circumference of the shell, and thus pressing the fabricagainst the internal circumference with the multi-ribbed structure, andcuring the belt matrix with the fabric. The fabric stretches toaccommodate itself to the multi-ribbed structure.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the present invention will be betterunderstood from the following description, with reference to theaccompanying drawings in which

FIG. 1 is a section view of a V-ribbed belt according to an embodimentof the invention, in a plane perpendicular to the belt longitudinaldirection.

FIG. 2 is a perspective view that schematically illustrates thearrangement of a mandrel and a shell which are used in the belt moldingof the embodiment.

FIG. 3 is an enlarged partial sectional view schematically showing thearrangement of the mandrel and shell along the radial direction beforethe curing process.

FIG. 4 is an enlarged partial sectional view schematically showing thearrangement of the mandrel and shell in the radial direction in thecourse of the curing process.

FIG. 5 schematically shows a sectional view of the arrangement formeasuring the extension properties of a woven fabric.

FIG. 6 shows plan views of a sheet of fabric used to determine a methodfor measuring the extension properties of the nylon woven fabric orknitted fabric used in the inventive and comparative examples.

FIG. 7 is a diagram showing the results of a tensile test in the axialdirection (i.e., in the belt lateral direction) on the sheet of fabricof Examples 1-6 and Comparative Examples 1 and 2.

FIG. 8 is a diagram showing the results of a tensile test in thecircumferential direction (i.e., in the belt longitudinal direction) onthe sheet of fabric of Examples 7-10 and Comparative Examples 3 and 4.

FIG. 9 is a layout of a running test machine used to test durabilityunder reverse bending.

FIG. 10 is a layout of a belt drive system on which Examples 17-21 andComparative Examples 5 and 6 were tested.

FIG. 11 illustrates the relationship between the fabric extension (%)and the coefficient of friction (COF) at the rib surface.

DETAILED DESCRIPTION

Embodiments of the present invention are described below with referenceto the drawings.

[First Embodiment]

FIG. 1 is a sectional view of a V-ribbed belt of the first embodiment,in a plane perpendicular to the belt longitudinal direction. Thestructure of the V-ribbed belt in the embodiment is described withreference to FIG. 1.

The V-ribbed belt 10 includes a rib-rubber layer 11 formed as amulti-ribbed structure, an adhesive rubber layer 13 in which tensilecords 12 are embedded, and a backing fabric 14 bonded to the back faceof the adhesive rubber layer 13. In addition, the surface of therib-rubber layer is covered with a fabric 15, such as woven fabric orknitted fabric.

The fabric 15 is selected from material with sufficient stretchability.Furthermore, the material is selected so as to afford sufficientdurability to the belt in consideration of the performance required ofthe rib surface (e.g., in terms of wear resistance, heat resistance,stability of friction coefficient, water resistance, and slip and noiseproperties).

For example, the material of the fabric 15 may include elastic yarn orfiber including polyurethane and at least one type of non-elastic yarnor fiber including cellulose- or non-cellulose-based yarn or fiber, or ablend thereof. The blend of cellulose-based yarn or fiber and thenon-cellulose-based yarn or fiber is made either by blending two typesof fibers in yarn spun or twist or by feeding different types of yarnsduring the fabric manufacturing process.

The cellulose-based yarn or fiber includes natural fiber includingcotton, linen, jute, hemp, abaca, and bamboo; man-made fiber includingrayon and acetate; and combinations thereof.

Non-cellulose-based yarn or fiber includes polyamide, polyester,polyethylene naphthalate, acrylic, aramid, polyolefin, polyvinylalcohol, liquid crystal polyester, polyether-etherketone, polyimides,polyketone, PTFE, e-PTFE, PPS, PBO, wool, silk and combinations thereof.

For improved wet performance, the fabric includes a two-yarnconstruction including a first yarn which is elastic such aspolyurethane, and a second yarn of cellulose such as cotton.Furthermore, a three or more yarn construction including an elastic yarnor fiber, a cellulose yarn or fiber, and other yarns, may be used. Athird yarn may be selected according to the desired wear resistance.

Namely, the first yarn is an elastic yarn such as polyurethane, whichprovides the fabric with a high level of stretchability. The second andthird yarn or fibers could consist of a blend of two different types ofyarn or fibers, which may be combinations of cellulose yarn or fiber andnon-cellulose yarn or fiber, blended in different ratios. One type isnon-cellulose yarn or fiber, which provides the wear resistance ordurability. The other type is cellulose yarn or fibers, which willprovide superior wet performance. In some applications the celluloseyarn or fiber alone can provide adequate durability and wet performance.

The blend ratio of cellulose-based yarn or fiber and non-cellulose-basedyarn or fiber may range from 100:0 to 0:100. A ratio of cellulose-basedyarn or fiber from 5% to 100% and non-cellulose-based yarn or fiber from0% to 95% is preferable. Furthermore, the ratio of the elastic yarn orfiber to the non-elastic yarn or fiber may be from 2% to 40%.

The process for manufacturing the V-ribbed belt 10, in which the moldingprocess is applied, will next be described with reference to FIGS. 2-4.FIG. 2 is a perspective view that schematically illustrates a mandrel(inner mold) and a shell (outer mold) for molding the V-ribbed belt 10in this embodiment. FIGS. 3 and 4 are enlarged partial sectional viewsof the mandrel and the shell along the radial direction, whichschematically illustrate their arrangement. FIG. 3 illustrates thearrangement before vulcanization and curing, and FIG. 4 illustrates thearrangement during vulcanization and curing.

A rubber pad 22 is arranged around the external circumference of thecylindrical mandrel 20, and belt materials 23 (including the backingfabric 14, an adhesive rubber matrix for forming the adhesive rubberlayer 13, the tensile cords 12, and a rib rubber matrix for forming therib rubber layer 11) are arranged around the outside of the rubber pad22. In addition, fabric 15 is arranged around the outside of the beltmaterials 23. In this embodiment, the fabric 15 is tubular and either ofseamless or seamed fabric. However, non-tubular fabric can also be usedby winding the fabric 15 around the mandrel 20 with both endsoverlapping. The mandrel 20, onto which both the belt materials 23 andfabric 15 are provided, is coaxially installed inside the cylindricalshell 21. At this time, a clearance d is interposed between the fabric15 and the internal circumference of the shell 21, as shown in FIG. 3.

In conjunction therewith, the fabric 15 is post-processed to enhance theperformance and the post-processing includes washing with hot water orchemicals, heat-setting, dying, adhesive treating, and laminating. Asfor the adhesive treating, an additional treatment using gum Arabic,adhesives such as RFL, and resin (for example, phenol or fluoric resin),is normally applied to the fabric 15 in order to enhance the adhesion ofthe fabric to the rubber material, or in order to obtain a performancecharacteristic required by the application. However, in some cases, nosuch additional treatment is applied.

The shell 21 has a number of grooves 21A in the form of a V-ribbedstructure on the internal circumference, wherein the grooves are alignedin the circumferential direction and are disposed in order to form themulti-ribbed structure of the V-ribbed belt 10. In the curing process,any suitable temperature-controlled fluid medium such as air, nitrogen,oil, water or steam is fed at high pressure between the rubber pad 22and the mandrel 20, so that the rubber pad 22 is expanded outwardly inthe radial direction. As a result, the belt materials 23 and the fabric15 are expanded outwardly in the radial direction, and thereby pressedagainst the internal circumference of the shell 21. In this process, thefabric 15 is deformed together with the rib-rubber layer 11 of the beltmaterial 23, and then crammed into the grooves 21A formed on theinternal circumference of the shell 21, thereby enabling a multi-ribbedstructure to be formed, as shown in FIG. 4. Moreover, the fabric 15 isin pressurized contact with, or bonded to the rib-rubber layer 11 in thecuring process, so that the fabric 15 and the surface of the rib-rubberlayer 11 become integrated.

Namely, the molding process according to the embodiment is carried outin the following steps: provide the belt material around the mandrel,cover the external circumference of the belt material with the fabric,install the mandrel (onto which both the belt material and the fabricare mounted) into the inside of the shell, and expand the belt materialand the fabric toward the internal circumference of the shell, thuskeeping them pressed against the multi-ribbed structure while the curingprocess is carried out. Incidentally, the belt matrix is cured after thepenetration of the belt matrix into the fabric.

In FIGS. 3 and 4, only three grooves 21A are shown. However, a pluralityof grooves is actually arranged over the entire internal circumferenceof the shell 21, as shown in FIG. 2. Moreover, the resulting piece witha multi-ribbed structure, prepared by the curing process, is removedfrom the shell 21 and cut along the ribs to a predetermined belt width,thereby producing a plurality of V-ribbed belts 10.

In the belt manufacturing process described above, both the beltmaterial 23 and the fabric 15 are radially expanded away from thecylindrical mandrel 20, thereby stretching the fabric 15 in thecircumferential direction of the cylindrical mold, that is, in the beltlongitudinal direction. At the same time, the deformation of both therib rubber and fabric 15 in accordance with the shape of grooves 21A inthe shell causes the fabric 15 to be stretched in the axial direction ofthe cylindrical mold, that is, in the belt lateral direction.

As shown schematically in FIG. 5, when it is assumed that the initialposition of the fabric 15 disposed around the mandrel 20 (i.e., theposition of the fabric 15 at the beginning of the molding process) is atradius R from the center of the mandrel 20 and that the distance betweenthe initial position of the fabric 15 and the bottom surface of thegroove 21A in the shell 21 (whose bottom surface corresponds to the ribtip of the V-ribbed belt) is D, then the length of the fabric 15 in thecircumferential direction (the belt longitudinal direction) changes fromthe initial radial distance 2πR to the elongated radial distance 2π(R+D). Accordingly, the extension of the fabric 15 in thecircumferential direction (i.e., the belt longitudinal direction) can berepresented by dividing the difference between the elongated radialdistance 2π (R+D) and the initial radial distance 2πR by the initialradial distance 2πR, giving D/R. Incidentally, the extension of thefabric in the circumferential direction includes the stretch needed tofit the mold.

On the other hand, the extension of the fabric 15 in the axial direction(i.e., in the belt lateral direction) can be expressed as (N×A−L)/L,where A is the profile length of a groove 21A along the axial direction(see FIG. 5); N is the number of ribs formed in the mold; and L is thelength of the grooved surface in the axial direction (i.e., the totallength in the belt lateral direction where the ribs are formed). Whenthe rib pitch p is employed, then L is expressed as L=N×p. Accordingly,the extension of the fabric in the axial direction (i.e., in the beltlateral direction) is found to be (A/p−1). Note that the profile lengthA corresponds to the length of one rib section, as shown by a thick linein FIG. 5, and the length A depends on the shape of the rib.

The extension of the fabric 15 in the circumferential and axialdirections should be values in which the fabric attached to the ribsurface maintains certain properties desired in the V-ribbed belt. Inthe first embodiment, the requirement that the fabric 15 maintaincertain properties in its role as the rib surface fabric necessitates,for instance, that the belt material 23 not fully penetrate the mesh ofthe fabric 15 during the pressurization.

In the manufacture of the V-ribbed belt implementing the molding processused in the embodiment, a fabric is used which shows an extensiongreater than D/R in the circumferential direction (i.e., in the beltlongitudinal direction), and an extension greater than (N×A−L)/L (orA/p−1) in the axial direction (i.e., in the belt lateral direction),under a particular condition (tension per unit width). Namely, astretchability range in either direction is defined so that the fabricwill maintain certain properties at the rib surface. Details of therange will be given afterward, referring to the comparison between theinventive and comparative examples.

A fabric that does not satisfy the above-mentioned extension in thecircumferential direction of the mandrel specified by both the shape ofthe rib and the dimensions of the mandrel in a given condition, maynevertheless be applied in some cases, when seamless or seamed tubularfabric is not used, by overlapping the ends of the fabric sheet or byallowing space, uncovered by the fabric, between the ends of the fabricsheet in the belt longitudinal direction.

On the other hand, if the fabric cannot be sufficiently stretched in theaxial direction of the mandrel, the fabric will not be displaced to theposition where it contacts the shell, despite being deformed along therib cavity of the shell. Furthermore, the rib rubber material will passthrough the mesh of the fabric, such that the rib rubber material willfill the shell mold. As a result, the fabric will be completely embeddedin the rib-rubber layer, such that the rib rubber directly forms the ribsurface. Therefore, in order to successfully manufacture themulti-ribbed belt by pressing the belt material against the shell andproducing a rib surface properly covered with fabric, as in the presentembodiment, it is necessary to use fabric with sufficient extensibilityat least in the axial direction (i.e., extensibility sufficient to allowthe fabric to contact the shell mold and deform into the shape of themold).

As for such fabric, the knitted fabric described above or a woven fabricmay be used. In the case of a woven fabric, one whose warp, weft, orboth, include an elastic yarn or textured yarn having undergone afinishing process such as curl-crimp finish, woolly finish, Taslanfinish, interlace finish, covering finish, etc., or some combinationthereof is used. Note that the above-mentioned extensibility is theminimum desired in the manufacturing process. Greater extensibilitywould actually be desired to satisfy the conditions of belt use. Forexample, additional extensibility would be desired in the beltlongitudinal direction for the belt to be flexible under small-pulleybending and reverse bending.

As described above, in accordance with the first embodiment, fabricsincluding woven or knitted fabric, which are more durable than non-wovenfabric, can be integrally provided on the rib surface, thereby improvingthe durability of the belt surface and the long-term maintenance of thebelt surface condition. Concomitantly, the slip and the generation ofabnormal sound are suppressed. In particular, the present embodimentallows the fabric to be integrally attached to the rib surface in theprocess of molding and curing, thereby effectively enhancing thedurability of the rib surface of the V-ribbed belt and maintaining thestate of the rib surface in the long-term.

In the following, the conditions for specifying the extensibility of thefabric in the first embodiment will be described, referring to inventiveand comparative examples.

EXAMPLES

First, it was examined as to whether the elongation or extension of thewoven nylon fabric and knitted nylon fabric used in the examplescoincided with the elongation defined by the dimensions of the moldapplied in the molding process. In this test, a sheet of woven fabricwas used in Example 3 and sheets of knitted fabric were used in Examples4-6.

In this confirmation test, a cross-mark with a length of 100 mm in boththe longitudinal and lateral directions was drawn on the sheet offabric, aligned to the axial and circumferential directions of themandrel. The fabric was applied around the belt material, which had beenpreviously applied around the mandrel, and then installed inside theshell, together with the mandrel. Then, the V-ribbed belt was formedwith these materials, utilizing the molding process. The process wascarried out under the conditions of (N×A−L)/L (or A/p−1)=0.8011 (80.11%)in the axial direction of the mandrel (i.e., in the belt lateraldirection), and D/R=0.0306 (3.06%) in the circumferential direction ofthe mandrel (i.e., in the belt longitudinal direction).

FIG. 6( a) is a schematic plan view of the unprocessed fabric sheet onwhich a cross-mark is drawn. FIG. 6( b) is a schematic plan view ofunwrapped processed fabric sheet on which the cross-mark is drawn. Afterthe extension of the fabric, a ruler was used to measure the lengths ofthe cross-mark arms. The length of the cross-mark in the circumferentialdirection (i.e., in the belt longitudinal direction) was 102-104 mm (anextension of 2-4%), and in the axial direction (i.e., in the beltlateral direction) it was 173.12-179.53 mm (an extension of73.12-79.53%). The extension of all the fabric sheets approximatelymatched these values.

FIG. 7 shows the results of a tensile test in the directioncorresponding to the axial direction of the mandrel (i.e., the beltlateral direction) for the sheets of fabric (woven and knitted) ofExamples 1-6 and Comparative Examples 1 and 2. The extension propertiesfor each test piece are shown in the diagram of FIG. 7, where theabscissa indicates the extension (%) and the ordinate indicates thetension (N) applied to the fabric per unit width (50 mm) in the tensiledirection.

Woven fabric was used in Examples 1-3 and in Comparative Example 1,while knitted fabric was used in Examples 4-6 and in Comparative Example2. The test pieces of Examples 1-6 gave the stretch propertiesrepresented by curves E1-E6, and the test pieces of Comparative Examples1 and 2 gave the stretch properties represented by curves C1 and C2.

Furthermore, using the fabric of Examples 1-6 and of ComparativeExamples 1 and 2, V-ribbed belts were formed with the molding process ofthe present embodiment under the conditions that the extension in theaxial direction (i.e., in the belt lateral direction) be (N×A−L)/L (orA/p−1)=0.8011 (80.11%). The V-ribbed surface was suitably covered withthe fabric in the molding using the fabric of Examples 1-6. However, asfor the fabric of Comparative Examples 1 and 2, the belt material passedthrough the mesh of the fabric during the pressurizing process so thatthe fabric was not left exposed at the rib surface.

Referring to the diagram of FIG. 7 and the molding test results of theV-ribbed belt of Examples 1-6 and Comparative Examples 1 and 2, it canbe appreciated that fabric with approximately 250 N/50 mm (the firstvalue) or less tension per unit width in the axial direction of themandrel (i.e., in the belt lateral direction) when the extension of thefabric in the axial direction (i.e., in the belt lateral direction) is(N×A−L)/L (or A/p−1), is preferable in order to achieve the desiredconditions of the fabric on the rib surface, in the case of the V-ribbedbelt manufactured by the molding process of the first embodiment.Namely, in the present examples, it is preferable to apply a fabric thatshows 250 N/50 mm or less tension per unit width when the extension isapproximately 80%. Moreover, in the present examples, the tension (perunit width) of the fabric is preferably 200 N/50 mm or less when theextension of the fabric in the axial direction (i.e., in the beltlateral direction) is approximately 80%. Note that these statements canbe interpreted as selecting fabric having an extensibility of 80% orgreater at 250 N/50 mm, and more preferably, at 200 N/50 mm, in theaxial direction (the belt lateral direction).

Referring to FIGS. 8 and 9, the relationship between the extension ofthe fabric in the circumferential direction (i.e., in the beltlongitudinal direction) and the durability of the belt subjected toreverse bending will be described next.

FIG. 8 is a diagram showing the results of a tensile test performed inthe circumferential direction of the mandrel (i.e., in the beltlongitudinal direction) for the woven and knitted fabric of Examples7-10 and Comparative Examples 3 and 4. The abscissa indicates theextension (%) and the ordinate indicates the tension (N) applied to thefabric per unit width (50 mm) in the tensile direction. Woven fabric wasused in Comparative Examples 3 and 4 and in Example 7, while knittedfabric was used in Examples 8-10. The extension properties of the testpieces of Examples 7-10 are indicated by curves E7-E10, respectively,whereas the extension properties of the test pieces of ComparativeExamples 3 and 4 are indicated by curves C3 and C4, respectively.

Similarly to Examples 1-6 and Comparative Examples 1 and 2, V-ribbedbelts were molded under the extension condition specified on thecircumferential direction (i.e., D/R=0.0306 (3.06%)), using fabrics withthe properties of those in Examples 7-10 and Comparative Examples 3 and4, in accordance with the molding process of the present embodiment. Inthis case, the V-ribbed belts were manufactured with a service lifeaimed at 500 hrs.

Next, a durability test (belt bending test) for a belt subjected toreverse bending was carried out on the V-ribbed belts that weremanufactured using the fabrics of Examples 7-10 and Comparative Examples3 and 4, applying a running test machine whose layout is illustrated inFIG. 9.

The running test machine of FIG. 9 was configured as a V-ribbed belt Bentrained around a drive pulley DR, a driven pulley DN, a tensionerpulley TEN, and three idler pulleys ID interposed respectively betweenthe pulleys DR, DN, and TEN. The drive pulley DR, the driven pulley DNand the tensioner pulley TEN had an effective diameter of 70.00 mm,whereas the idler pulleys ID had an effective diameter of 52.00 mm. Therunning test machine was operated at an ambient temperature of 100° C.,wherein the drive pulley DR was rotated at 5,200 rpm, and wherein theaxial load of the belt was 588 N.

In the running test of the V-ribbed belts of Comparative Examples 3 and4, cracks appeared within 24 hrs and the test was stopped after 328.4and 166.4 hr runs, respectively, when either a rib broke or a largenumber of cracks formed. On the other hand, in the case of the V-ribbedbelts of Examples and 8, cracks appeared after 305 and 524.2 hrs,respectively. The test run on the V-ribbed belt of Example 7 was stoppedat the 650-hr mark, when the number of cracks reached the number of ribsplus one. However, for the V-ribbed belt of Example 8, only three crackswere found after 1003.7 hrs of running. Furthermore, as for Examples 9and 10, no cracks were detected even after running 400 hrs.

Thus, satisfactory durability resistance against belt reverse bendingwas obtained with the belt using the fabric of Examples 7-8, but notthat of Examples 3 and 4. Therefore, from the diagram of FIG. 8, it canbe appreciated that for the fabric to give satisfactory durabilityagainst reverse bending, it should preferably be selected from amongfabrics that shows approximately 50N/50 mm (the second value) or lesstension per unit width in the circumferential direction of the mandrel(i.e., in the belt longitudinal direction) when the extension in thecircumferential direction (i.e., in the belt longitudinal direction) isdefined as R/D. Namely, in the present examples, the tension of thefabric in the circumferential direction (i.e., in the belt longitudinaldirection) per unit width should preferably be 50N/50 mm or less whenthe extension in the circumferential direction (i.e., in the beltlongitudinal direction) is approximately 3%. This statement may beinterpreted as selecting fabric having an extensibility of 3% or greaterat 50N/50 mm in the circumferential direction (the belt longitudinaldirection).

Referring to Tables 1-3, the results of the slip and noise test for theV-ribbed belt of Inventive Examples 11-16 (Ex-11 to Ex-16) andComparative Examples 5 and 6 (CE-5 and CE-6) are discussed.

Table 1 shows the properties of the fabric used in Examples 11-16.Examples 11-16 are the V-ribbed belt whose ribbed surface was coveredwith knitted fabric. On the other hand, the ribbed surface ofComparative Example 5 was covered with tissue (non-woven fabric), andthe ribbed surface of Comparative Example 6 was ground and no fabric wasapplied. The fabric of Examples 11-14, and 16 contained 15% polyurethane(elastic yarn), and Example 15 contained 30% polyurethane with theremainder non-elastic yarn. As for the non-elastic yarn, Examples 11-13and 16 contained cellulose yarn, such as cotton, and Examples 12-15contained non-cellulose yarn, such as PET or PA. Namely, Examples 11 and14-16 had a two-yarn construction and Examples 12 and 13 had athree-yarn construction. The blend ratio of Table 1 shows the ratio ofthe cellulose yarn to the non-cellulose yarn for the balance excludingthe PU content (elastic yarn). Furthermore, the longitudinal elongation(extension), the lateral elongation in percentage at 9.807N/25 mm foreach fabric, and the thickness (mm) are listed in Table 1. Note that thefabric with the stretchability greater than 80% at 9.807N/25 mm width inthe belt lateral direction and greater than 10% at 9.807N/25 mm width inthe belt longitudinal direction is used.

TABLE 1 CE-5 CE-6 Ex-11 Ex-12 Ex-13 Ex-14 Ex-15 Ex-16 Rib-coverageTissue ground knit knit knit knit knit knit PU content N/A N/A 15% 15%15% 15% 30% 15% Cellulose yarn N/A N/A cotton cotton cotton — — cottonNon-cellulose yarn N/A N/A — PET PA PET PA — Blend ratio N/A N/A — 50:5050:50 — — — Longitudinal N/A N/A 400 433 400 270 250 380 elongation at9.807N/25 mm, (%) Lateral N/A N/A 320 320 400 125 125 255 elongation at9.807N/25 mm, (%) Fabric thickness, mm N/A N/A 0.9 1.0 1.0 1.1 0.9 1.1

Table 2 gives the specifications of the V-ribbed belt prototypes used inExamples 11-16 and Comparative Examples 5 and 6. The lateral elongation(extension) and the longitudinal elongation are the extensions in eachdirection after the knitted fabric was applied on the belt.

TABLE 2 CE-5 CE-6 Ex-11 Ex-12 Ex-13 Ex-14 Ex-15 Ex-16 Belt length, mm1000 1035 1000 1000 1000 1000 1000 1000 Lateral N/A N/A 80.0 80.0 80.080.0 80.0 80.0 elongation, % Longitudinal N/A N/A 18.6 21.4 20.6 11.611.4 17.2 elongation, %

The results of the slip and noise test are shown in Table 3.

TABLE 3 CE-5 CE-6 Ex-11 Ex-12 Ex-13 Ex-14 Ex-15 Ex-16 New Slip N Y N N NN N N Noise ⊚ Δ ⊚ ⊚ ⊚ ◯ ◯ ⊚ Conditioned Slip N Y N N N Y N N Noise Δ X ⊚⊚ ⊚ Δ Δ ⊚ X: over 100 dB noise Δ: 90 dB-100 dB noise ◯: 80 dB-90 dBnoise ⊚: below 80 dB

As shown in Table 3, Examples 11-13 and 16, inclusion of the celluloseyarn (cotton) gave good results in both slip and noise performance forboth the new and conditioned V-ribbed belt.

Referring to Tables 4-6 and FIG. 10, the results of the noise controldurability test are next explained. Table 4 shows the properties of thefabric used in Inventive Examples 17-21, as in Table 1. Furthermore,Table 5 shows the specification of the prototype V-ribbed belt used inExamples 17-21, as in Table 2. Namely, each of the items in Tables 4 and5 are the same as those in Tables 1 and 2. In this test, Examples 17-21were compared with Comparative Examples 5 and 6, whose property andspecification are referred to in Tables 1 and 2.

TABLE 4 Ex-17 Ex-18 Ex-19 Ex-20 Ex-21 Rib-coverage knit Knit knit knitknit PU content 15% 15% 15% 15% 15% Cellulose yarn cotton Cotton cotton— — Non-cellulose yarn — PET PA PET PA Blend ratio — 50:50 50:50 — —Longitudinal 400 433 400 400 400 elongation at 9.807N/25 mm, (%) Lateral320 320 400 400 400 elongation at 9.807N/25 mm, (%) Fabric thickness, mm0.9 1.0 1.0 1.1 0.9

TABLE 5 Ex-17 Ex-18 Ex-19 Ex-20 Ex-21 Belt length, mm 1510 1510 15101510 1510 Lateral 80.0 80.0 80.0 80.0 80.0 elongation, % Longitudinal 6565 65 65 65 elongation, %

FIG. 10 shows the layout of a belt drive system on which Examples 17-21and Comparative Examples 5 and 6 were tested. The noise controldurability test was carried out on an actual engine accessory drivesystem. The V-ribbed belts were entrained around a crankshaft pulleyCRK, a tensioner pulley TEN, an alternator pulley AL1, a power steeringpump pulley P_S, an idler pulley IDR, and an air conditioner pulley A_C.The engine speed was set to an idle speed with engine unloaded (in Park)and the alternator was loaded to 100% duty. The pulley P_S was offset 4mm from the coplanar position, which generated two degrees of beltmisalignment angle.

Water was applied to the belt once every 4 hours at the entry of thepower steering pump pulley P_S (indicated by arrow Aw). The test wascarried out under ambient temperature until noise was detected.

The results of the noise control durability test are shown in Table 6with numerals indicating actual hours transpired until noise onset foreach example. As shown in Table 6, Examples 17-19 which includecellulose yarn, such as cotton yarn, showed good performance in noisecontrol durability.

TABLE 6 CE-5 CE-6 Ex-17 Ex-18 Ex-19 Ex-20 Ex-21 Noise 5.2 2 100 70 40 024.5 Evaluation Rate

Referring to Tables 7-9, the results of the slip and noise performancetest for an inventive V-ribbed belt in which a seamless woven fabrictube was applied will be explained next. Table 7 shows the properties ofthe seamless woven fabric used in Inventive Example 22 and the seamedwoven fabric used in Comparative Example 7 (CE-7), in the style ofTable 1. The fabric of Example 22 included 28% elastic yarn (PU) withthe remainder a cellulose-based yarn (cotton), while Comparative Example7 included neither. Table 8 shows the prototype specification of theV-ribbed belt applied in Examples 22 and Comparative Example 7, in thestyle of Table 2.

TABLE 7 CE-7 Ex-22 rib-coverage woven woven PU content — 28% celluloseyarn — cotton non-cellulose yarn PA PA warp yarn PA PA/PU weft yarn PACotton/PU Longitudinal 80 116 elongation at 9.807N/25 mm, (%) Lateral 50140 elongation at 9.807N/25 mm, (%) Fabric thickness, mm 0.6 1.06

TABLE 8 CE-7 Ex-22 Belt length, mm 1000 1000 Lateral 80 80 elongation, %Longitudinal 5.0 14.4 elongation, %

As shown in Table 9, although slip did not occur for either Example 22or Comparative Example 7, there was a significant difference in thenoise performance of the new belt compared to the conditioned belt.Namely, Example 22 showed better noise performance than ComparativeExample 7.

TABLE 9 CE-7 Ex-22 New Slip N N Noise Δ ⊚ Conditioned Slip N N Noise X ⊚X: over 100 dB noise Δ: 90 dB-100 dB noise ◯: 80 dB-90 dB noise ⊚: below80 dB

As described above, the first embodiment used a fabric with an extensionproperty in which the tension of the fabric is less than or equal to afirst value when the extension in the axial direction of the mandrel(i.e., in the belt lateral direction) is defined as (N×A−L)/L or(A/p−1), in order to maintain the desired condition of the fabric on therib surface (e.g. the condition that the fabric completely cover the ribsurface). Furthermore, in consideration of the durability under reversebending, the fabric used should exhibit a tension less than or equal toa second value when the extension in the circumferential direction(i.e., in belt the longitudinal direction) is defined as R/D.

Note that when knitted fabric is used instead of woven fabric, theknitted fabric should have a similar stretchability to the woven fabric(e.g., knitted of similar material and subjected to similar treatment).In this case, the knitting should be such that the knitted fabric showsthe required extensibility in both directions (belt longitudinal andlateral directions). For example, weft-knitted fabric may be used, whichgives good two-way extensibility. Furthermore, the weft-knitted fabricmay be of a seamless tubular type. In addition, unevenness on the ribsurface resulting from seams or the overlap of the fabric sheet can beavoided by using seamless knitted fabric.

[Second Embodiment]

In the following, a V-ribbed belt according to the second embodiment ofthe invention will be described. The V-ribbed belt according to thesecond embodiment is manufactured using almost the same method as in thefirst embodiment. However, as for the V-ribbed belt according to thesecond embodiment, the belt material 23 penetrates the mesh of fabric 15to a chosen depth. In so doing, the condition of the fabric 15 on therib surface is maintained while the characteristics (coefficient offriction, wear resistance, etc.) of the rib surface can be controlled bythe amount of rib rubber material that has passed through the mesh ofthe fabric 15.

Namely, the rib rubber material that has passed through the mesh of thefabric 15 forms the rib surface in cooperation with the fabric 15, andtherefore both the coefficient of friction and the durability of the ribsurface are directly affected by the amount of rib rubber material thathas fully penetrated the mesh of the fabric 15. Furthermore, thepenetration of the rib rubber material through the fabric is affected bythe extension of the fabric 15.

Accordingly, a V-ribbed belt with desired rib surface characteristicsmay be obtained by selecting a woven fabric or knitted fabric havingextension properties in the belt longitudinal and belt lateraldirections based on the extension specified by the shape of the belt andthe characteristics required for the rib surface, wherein the rib rubbermaterial passes through the mesh of the fabric to a predeterminedextent. Note that the extension property of the fabric used in the aboveselection may be determined with reference to the first value and/or thesecond value of the fabric tension induced when the fabric is stretchedto the above extension. Furthermore, the other properties of the fabric,such as mass per unit area, density, the characteristics of the yarn orfilament (including thickness, finish, yarn density, yarn size, andfabric permeability upon stretching, etc.) and so on, can also besuitably selected in order to control the above-mentioned coefficient offriction and wear resistance. Incidentally, molding pressure is anotherprocess variable.

EXAMPLES

A rib surface with more matrix penetration will have a highercoefficient of friction, thus the coefficient of friction at the ribsurface is indicative of the degree of matrix penetration. Table 10 andFIG. 11 illustrate the relationship between the fabric extension (%) andthe coefficient of friction (COF) at the rib surface.

In the test, tubular knit fabric was prepared in differentcircumferences and stretched to different levels to fit onto a 1510 mmmold. The fabric was then stretched to different degrees in order toachieve different coefficients of friction, and the coefficient offriction was then measured. Incidentally, the fabrics of Examples 23-26included PET and cotton yarn.

TABLE 10 Ex-23 Ex-24 Ex-25 Ex-26 Rib-coverage PET/ PET/ PET/ PET/ cottonknit cotton knit cotton knit cotton knit Knit tube OC, mm 1372 1209 1077914 % fabric stretch 10 25 40 65 COF 0.87 1.04 1.14 1.69 OC: outercircumference

As shown in FIG. 11 and Table 10, the coefficient of friction at the ribsurface increases as the extension of the fabrics increase. Namely, byselecting the fabric stretchability, the penetration of the matrix canbe indirectly controlled and in turn the coefficient of friction at therib surface can be controlled.

Note that in the present application, the term “penetrate” includes bothpermeation of rubber into the fabric texture and penetration where therubber passes through the mesh of the fabric. In addition, the phrases“does not penetrate” and “does not fully penetrate” describe permeationwhere the rubber does not pass through the mesh to the other side.

Although the embodiments of the present invention have been describedherein with reference to the accompanying drawings, obviously manymodifications and changes may be made by those skilled in this artwithout departing from the scope of the invention.

What is claimed is:
 1. A V-ribbed belt, comprising a ribbed surfacecovered with weft-knitted fabric, said weft-knitted fabric beingstretchable in two predetermined directions; wherein said weft-knittedfabric comprises elastic yarn and at least one type of non-elastic yarn;and said non-elastic yarn comprises cellulose-based fiber or yarn;wherein said elastic yarn comprises polyurethane; and wherein saidweft-knitted fabric is a two-yarn construction consisting of a cottonyarn and a polyurethane yarn.
 2. The V-ribbed belt according to claim 1,wherein said weft-knitted fabric is post-processed to enhance theperformance and said post-processing comprises one or more of: washingwith hot water or chemicals, heat-setting, dying, adhesive treating, andlaminating.
 3. The V-ribbed belt according to claim 1, wherein saidweft-knitted fabric is made by feeding separately said elastic yarn andsaid non-elastic yarn during the fabric manufacturing process.
 4. TheV-ribbed belt according to claim 1, wherein said weft-knitted fabric isseamless tubular weft-knitted fabric.
 5. The V-ribbed belt according toclaim 1; wherein one of said two predetermined directions corresponds tothe belt lateral direction and the other corresponds to the beltlongitudinal direction, wherein the stretchability of said fabric isgreater than 80% at 9.807N/25 mm width in the belt lateral direction andgreater than 10% at 9.807N/25 mm width in the belt longitudinaldirection.
 6. The V-ribbed belt according to claim 5, wherein thestretchability of said fabric is at least 116% at 9.807N/25 mm width inthe belt lateral direction and at least 116% at 9.807N/25 mm width inthe belt longitudinal direction.
 7. The V-ribbed belt according to claim5, wherein the tension per unit width of the fabric in the belt lateraldirection is less than or equal to a first value when the extension ofsaid fabric in the belt lateral direction has a value equal to theprofile length of one rib in the belt lateral direction divided by therib pitch, minus one.
 8. The V-ribbed belt according to claim 7, whereinthe tension per unit width of the fabric in the belt longitudinaldirection is less than or equal to a second value when the extension ofsaid fabric in the belt longitudinal direction has a value equal to thelength of a rib tip in the belt longitudinal direction during molding ina shell having rib-forming grooves on the internal circumferencethereof, minus the length of said fabric in the belt longitudinaldirection at the beginning of the molding process, divided by the lengthof said fabric in the belt longitudinal direction at the beginning ofthe molding process.
 9. The V-ribbed belt according to claim 8, whereinsaid first value is approximately 250N/50 mm, and said second value isapproximately 50N/50 mm.
 10. The V-ribbed belt according to claim 6,wherein said fabric is stretchable at least 140% at 9.807N/25 mm widthin at least one of said two predetermined directions.